This invention is generally directed to layered hydrogenated amorphous silicon imaging members; and more specifically, the present invention is directed to layered photoconductive imaging members comprised of hydrogenated amorphous silicon and certain charge transport layers. Therefore, in one embodiment of the present invention, there is provided a layered photoresponsive imaging member comprised of a supporting substrate, hydrogenated amorphous silicon, and in contact therewith a transport layer comprised of very specific components inclusive of nitrides, phosphides, and oxides, such as silicon nitride, boron phosphide, and boron oxide. Further, in an alternative specific embodiment of the present invention there is provided a layered photoresponsive imaging member wherein the specific charge transport layer is situated between the supporting substrate and the photoconductive hydrogenated amorphous silicon layer. These imaging members can be incorporated into electrophotograpic, and in particular xerographic imaging and printing systems wherein, for example, the latent electrostatic patterns which are formed can be developed into images of high quality and excellent resolution. Moreover, the members of the present invention possess high charge acceptance values corresponding to electric fields in excess of 50 volts per micron (50 v/.mu.m); and further these members can be of a very desirable thickness from, for example, about 10 microns or less. Also, the imaging members of the present invention have desirable low dark decay properties enabling them to be very useful in xerographic imaging processes. In these processes, latent electrostatic images are formed on the devices involved, followed by development, transfer and fixing. Additionally, the photoresponsive imaging members of the present invention, when incorporated into xerographic imaging and printing systems; are insensitive to humidity and corona ions permitting the formation of acceptable images of high resolution for an extended number of imaging cycles.
Electrostatographic imaging, particularly xerographic imaging processes, are well known, and are extensively described in the prior art. In these processes a photoconductor material is selected for forming the latent electrostatic image thereon. The photoreceptor is generally comprised of a conductive substrate containing on its surface a layer of photoconductive material; and in many instances, a thin barrier layer is situated therebetween to prevent charge injection from the substrate, which injection could adversely effect the quality of the resulting image. Examples of known useful photoconductive materials include amorphous selenium, alloys for selenium such as selenium-tellurium, selenium-arsenic, and the like. Additionally, there can be selected as the photoresponsive imaging member various organic photoconductive materials including, for example, complexes of trinitrofluorenone and polyvinylcarbazole. Recently there has been disclosed layered organic photoresponsive devices with aryl amine hole transporting molecules, and photogeneratig layers, reference U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference.
Also known are amorphous silicon photoconductors, reference for example U.S. Pat. Nos. 4,265,991 and 4,225,222. There is disclosed in the '3 991 patent an electrophotographic photosensitive member comprised of a substrate, and a photoconductive overlayer of amorphous silicon containing 10 to 40 atomic percent of hydrogen and having a thickness of 5 to 80 microns. Additionally, this patent describes several processes for preparing amorphous silicon. In one process embodiment, there is prepared an electrophotographic photosensitive member by heating the member present in a chamber to a temperature of 50.degree. C. to 350.degree. C., introducing a gas with silicon and hydrogen atoms, providing an electrical discharge in the chamber by electric energy to ionize the gas, followed by depositing amorphous silicon on an electrophotographic substrate at a rate of 0.5 to 100 Angstroms per second by utilizing an electric discharge thereby resulting in an amorphous silicon photoconductive layer of a predetermined thickness. Although the amorphous silicon device described in this patent is photosensitive, after a minimum number of imaging cycles, less than about 100 for example, unacceptable low quality images of poor resolution with many deletions may result. With further cycling, that is subsequent to 100 imaging cycles and after 1,000 imaging cycles, the image quality may continue to deteriorate often until images are completely deleted.
Further, there is disclosed in the prior art amorphous silicon photoreceptor imaging members containing, for example, stoichiometric silicon nitride overcoatings; however, these members in some instances generate prints of low resolution as a result of the electric field induced lateral conductivity in the photogenerator layer. Additionally, with the aforementioned silicon nitride overcoatings, the resolution loss can in many instances be extreme thereby preventing, for example, any images formation whatsoever.
Other representative prior art disclosing amorphous silicon imaging members, including those with overcoatings, are U.S. Pat. Nos. 4,460,669; 4,465,750; 4,394,426; 4,394,425; 4,409,308; 4,414,319; 4,443,529; 4,452,874; 4,452,875; 4,483,911; 4,359,512; 4,403,026; 4,416,962; 4,423,133; 4,460,670; 4,461,820; 4,484,809; and 4,490,453. Additionally, patents that may be of background interest with respect to amorphous silicon photoreceptor members include, for example, U.S. Pat. Nos. 4,359,512; 4,377,628; 4,420,546; 4,471,042; 4,477,549; 4,486,521; and 4,490,454.
Further, additional representative prior art patents that disclose amorphous silicon imaging members include, for example U.S. Pat. No. 4,357,179 directed to methods for preparing imaging members containing high density amorphous silicon or germanium; U.S. Pat. No. 4,237,501 which discloses a method for preparing hydrogenated amorphous silicon wherein ammonia is introduced into a reaction chamber; U.S. Pat. Nos. 4,359,514; 4,404,076; 4,403,026; 4,397,933; 4,423,133; 4,461,819; 4,237,151; 4,356,246; 4,361,638; 4,365,013; 3,160,521; 3,160,522; 3,496,037; 4,394,426; and 3,892,650. Of specific interest are the amorphous silicon photoreceptors illustrated in U.S. Pat. No. 4,510,224, which discloses an electrophotographic photoreceptor comprising a hydrogenated amorphous silicon carbide transport layer 2 formed below a photoconductive layer 3, reference FIG. 5; U.S. Pat. No. 4,518,670 directed to an electrophotographic member comprising a transport layer 2 with at least one atomic percent nitrogen present therein, see FIGS. 1 to 4; and U.S. Pat. No. 4,495,262 describing an electrophotographic photosensitive member comprising two amorphous hydrogen silicon carbide layers 2 and 4, one on each side of the photoconductive layer 3, refrence FIGS. 1 and 2. Additionally, processes for depositing large area defect free films of amorphous silicon by the glow discharge of silane gases are described in Cittick et al., the Journal of the Electrochemical Society, Volume 116, Page 77, (1969). Further, the fabrication and optimization of substrate temperatures during amorphous silicon fabrication is illustrated by Walter Spear, the Fifth International Conference on Amorphous and Liquid Semiconductors presented at Garmisch Partenkirchen, West Germany in 1963. Other silicon fabrication processes are described in the Journal of Noncrystalline Solids, Volumes 8 to 10, Page 727, (1972), and the Journal of Noncrystalline Solids, Volume 13, Page 55, (1973).
There are also illustrated in copending applications photoconductive imaging members comprised of amorphous silicon. Accordingly, for example, there is illustrated in copending application U.S. Ser. No. 695,990, entitled Electrophotographic Devices Containing Compensated Amorphous Silicon Compositions, the disclosure of which is totally incorporated herein by reference, an imaging member comprised of a supporting substrate and an amorphous hydrogenated silicon composition containing from about 25 parts per million by weight to about 1 percent by weight of boron compensated with substantially equal amounts of phosphorus. Furthermore, described in copending application U.S. Ser. No. 548,117, entitled Electrophotographic Devices Containing Overcoated Amorphous Silicon Compositions, the disclosure of which is totally incorporated herein by reference, are imaging members comprised of a supporting substrate, an amorphous silicon layer, a trapping layer comprised of doped amorphous silicon, and a top overcoating layer of stoichiometric silicon nitrides. More specifically, there is disclosed in this copending application an imaging member comprised of a supporting substrate, a carrier transport layer comprised of uncompensated or undoped amorphous silicon; or amorphous silicon slightly doped with p or n type dopants such as boron or phosphorus, a thin trapping layer comprised of amorphous silicon which is heavily doped with p or n type dopants such as boron or phosphorus; and a top overcoating layer of specific stoichiometric silicon nitride, silicon carbide, or amorphous carbon. However, one disadvantage with this imaging member is that the trapping layer introduces a dark decay component which reduces the charge acceptance for the imaging member.
Additionally, described in copending application U.S. Ser. No. 662,328 entitled Heterogeneous Electrophotographic Imaging Members of Amorphous Silicon, the disclosure of which is totally incorporated herein by reference, are imaging members comprised of hydrogenated amorphous silicon photogenerating compositions, and a charge transporting layer of plasma deposited silicon oxide containing at least 50 atomic percent of oxygen. The imaging member of the present invention is comprised of similar components with the exception of the selection of the charge transporting layer compounds selected.
Although the above described amorphous silicon photoresponsive members, particularly those disclosed in the copending applications, are suitable, in most instances, for their intended purposes there continues to be a need for improved members comprised of amorphous silicon. Additionally, there is a need for amorphous silicon imaging members that possess desirable high charge acceptance values, low charge loss characteristics in the dark, improved adhesion characteristics, and excellent transport of electrical charges. Furthermore, there continues to be a need for improved amorphous silicon imaging members with specific charge transport layers. Also, there is a need for hydrogenated amorphous silicon imaging layers with transport layers of specific nitrides, phosphides and oxides. Further, there is a need for imaging members with the aforementioned charge transport layers, and where there is introduced therein electronic defect states by the stoichiometric control of constituent materials of sufficient density enabling transport to be accomplished by hopping between the resulting localized states. These states are positioned in the band gap of the charge transport component thus permitting the efficient injection of carriers from the amorphous silicon photogenerating layer by the choice of the defect state, and by, for example compositional grading of the interface between the photogeneration and transport layers. Furthermore there is a need for amorphous silicon imaging members with the property of low surface potential decay rates in the dark, and photosensitivity in the visible and the near visible wavelength range. There is also a need for hydrogenated amorphous silicon imaging members with improved mechanical characteristics such as the ability to bend over small radii, and which imaging members permit excellent adhesion of the layers to the substrate. Furthermore, there is a need for imaging members with improved charge transport characteristics thereby permitting the residual voltage after optical exposure to be of a relatively small value, that is from about 0 volts to about 10 volts, which voltage remains substantially constant upon repeated cycling of the imaging member.